The present invention relates to material handling vehicles, and more particularly to systems and methods for mast oscillation damping for material handling vehicles.
Material handling vehicles (MHV), such as lift trucks, forklift trucks, reach trucks, turret trucks, side loader trucks, counterbalanced lift trucks, pallet stacker trucks, orderpickers, transtackers, and man-up trucks, can be commonly found in warehouses, factories, shipping yards, and, generally, wherever pallets, large packages, or loads of goods can be required to be transported from place to place.
Often, MHVs can be high-lift vehicles that can be capable of manipulating loads at higher elevations. Undesirable oscillations may occur in the mast or other vertical weight-bearing portion of high-lift vehicles when operating at high elevations. For example, mast oscillations may be caused by accelerating or decelerating the body 102 and/or raising or lowering a load on a fork assembly when the MHV can be operating at higher elevations. These mast oscillations can increase the time required to pick a load from a rack or to place a load onto a rack as an operator of a manned MHV may have to wait until the oscillations cease or can be small enough as to enable accurate picking or placing of the load. Additionally, mast oscillations can, in some instances, increase wear on the MHV.
A previous solution for reducing mast oscillations utilizes the traction system to introduce counter impulse forces in the traction system to cancel mast oscillations. The traction motor accelerates or decelerates in forward or backward directions to cancel the mast oscillations. However, in such an approach, the perturbations imposed by the traction motor will cause the MHV to move fore and aft in conflict with a position hold algorithm. This can cause the MHV to move to a position away from where the operator intended the MHV to remain.
Another previous solution for reducing mast oscillations utilizes reach actuators of a moving-mast type reach MHV to move the entire vertical mast fore and aft to damp mast oscillations. However, such an approach can be not applicable for reach trucks that utilize a pantograph- or scissor-type reach mechanism instead of moving mast. Further, in a reach truck application setting, such a previous approach provides an inefficient control mechanism in that oscillations induced by a load or assembly situated at the top of a mast can be controlled by movements at the bottom of the mast.
Though suitable for some application settings, such previous solutions do not meet the needs of all application settings and/or users. For example, a desire may exist for an oscillation reduction mechanism that overcomes the aforementioned issues by, in certain embodiments, enabling its corresponding use with position hold algorithms and by enabling oscillation reduction with scissor-type reach trucks.